Method of casting refractory metals



1Q6 84 CROSS REFERENCE EXAMINEI U f 5f Oct. 9, 1934. E. A. DE BATS1,976,009

METHOD OF CASTING REFRACTORY IBTALS Filed Oct. 15. 1932 I IN NTO [Hf/1W5A 54 ATTORNEYS Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE EtienneA. Do Bats, Millbnrn, N. J.

Application October 15, 1932, Serial No. 637,951

8 Claims. (01. 25-193) This invention relates to improvements in Thepatterns of fusible metal are accurately methods and apparatus forcasting refractory metal compositions in a variety of simple and/orintricate forms, some of which may have convoluted and/or undercutsurfaces.

Hitherto, in the preparation of hard wearing machine elements, such asimpeller blades for screw pumps, mesh gears and the like, it has beennecessary to carry out the forming operations by means of machinecutting tools and/or grinders. With the advent of wear resistantmaterials, such as tungsten carbide and like mineralogically hardmaterials, attempts have been made to form involved or intricatelyshaped articles without success, due to the lack or workability of thematerials and to the further fact that machine cutting tools andgrinding wheels are not available with sumcient hardness to successfullyattack such materials on a production basis. The use of diamond dust, asan abrasive, while possible, is commercially impractical with suchmaterials, due to the rapid wear and loss of abrasive.

It has now been found possible to prepare wear resistant convoluted andother intricately shaped tools, wearing parts, screw pump members andthe like from compositions which include exceptionally high wearresisting materials such as tungsten carbide and alloys of the same,with any of iron, cobalt, nickel, as alloying metals, and with orwithout the inclusion of tantalum metal, chromium, molybdenum and thelike, all in metallic form.

The novel process of the present invention comprehends the preparationor forming of an exact copy or duplicate of the article to be formed,either by machining, grinding, casting in plaster of Paris or likecasting material, or in any other manner, well known to pattern makersand others skilled in the art. These patterns are preferably made of afusible metal or metals, such as lead, zinc, tin, bismuth and any oftheir alloys, such as Woods metal, type metal and solders of varyingdegrees of hardness. The pattern of the article to be duplicated in thewear resistant composition or compositions is formed from such lowmelting or fusible compositions, as they will hereinafter be referred tofor sake of clarity, and to differentiate them from tungsten carbidecompositions, and the like, which are substantially infusible attemperatures commercially available. The fusion temperature of tungstencarbide and like compounds of high wear resistance is well above 2000C., and furnace installations capable of retaining any such heat areextremely costly.

prepared, as intimated above, either by machining or in any othersuitable manner, and these members are thereafter placed in a suitablemold such as a multi-partite mold comprising a series or plurality ofinterlocking tubes of any desired shape and diameter. The patterns aremounted on a suitable supporting block and disposed inwardly of the moldmembers so as to be equally spaced from all sides. Thereafter, a mlgingcompound, such as Fulverizeg silica or any other mes-eta materia preerably as finely powed or da around the atan extremely'fi'z'i'fiiflicefinish is es red on the finished article, the refractory aterial used inthe mold should be ground as finely as possible, preferably in the formknown commercially as-fioun- The refractory mix material is filled intothe sheath or mold casing and tamped or compressed into position by theplunger. This operation is preferably carried out in stages, a smallamount of mold material being introduced into the mold and compressedand this step being repeated until the pattern is completely incased ina compacted mold mass. This is continued further to insure properdensifying of the material and to make sure that the top portions of thepattern are uniformly supported. Any excess of mold material will findits way into the center of the hollow piston or plunger on the finalcompression, due to the lack of lateral support, as afforded in theprior stages by the body of the pattern.

The high compression of the material compacts it to an extraordinarydegree and, due to this high pressure, plus the fineness of thematerial, the surfaces of the mold material contacting with the surfacesof the pattern take on a smooth finish, substantially free from voidsand any and all irregularities. The finish so imparted is so fine thatcast articles later prepared therefrom require only a lap or finishgrinding in 100 order to be rendered suitable for use.

When the mold composition has been compressed into place and to adesired degree, the plunger, and the superposed mold sections, fromwhich the excess mold material has been pressed, 105

are removed. The mold sheath, with its contained compressed moldmaterial, and associated fusible metal pattern, is then introduced intoa core ov her suitable ting device, and baked to decompose inder andcause the 110 mold material to set to a hard mass. During this baking,the metal of the fusible pattern is melted and flows out of the moldassembly, leaving a cavity whose surfaces are the exact replica of thearticle which is to be cast.

While pressures of 50 to tons per sq. in. have been indicated asdesirable, the particular pressure used will depend upon the materialsto be cast. and also upon the texture or finish of the surface of themold. In this connection, it is to be noted that the higher thecompression to be applied in the mold forming step, the less binder willbe used with the pulverized refractory material. Thus, where pressuresof the order of 100 tons per sq. in. are to be used, it will besufficient to merely dampen the particles while, if much lower pressuresare to be used, more binding agent will be needed in admixture with therefractory particles.

The mold assembly, after baking, and while still hot, is then insertedin a suitable holder and the latter, with a desired number of likedevices,

may be inserted in a centrifugal casting machine, care being taken tobalance the mold containers. Suitable inserts such as shafts of steel orother suitable metals may be set in the mold, after melting out thepattern and the refractory metal compositions subsequently casttherearound. The casting machine may then be set in operation and a massof a refractory material, which has .previously been brought to adesired heat, that is, of the order of incipient fusion, is placedtherein. The mass of refractory material still retains its solidstructure and may be lifted from the furnace or crucible with tongs, andafter dropping into the casting machine will be instantly forced intothe mold cavities.

Under ordinary methods of centrifugal casting, pressures exerted by themetal upon the refractory mold material may approach 5 to 6 tons per sq.in., although, it will, of course, be understood that any desiredpressure may be attained by suitably designing the centrifugal machineand its driving motor or source of power.

The casting of a refractory metal composition, under pressures of theorder of 2 to 10 tons per sq. in., and preferably of 5 to 6 tons per sq.in. into and against mold surfaces which have been formed underpressures of the order of 50 to 100 tons per sq. in. will obviously notintroduce any difficulties in the way of the scouring, washing, workingor gouging out of mold surfaces, nor of the disintegration of the sameby centripetal forces, so that the cast articles will be accurately andcompletely conformed to unmarred mold surfaces.

After the casting operation has been completed, the mold assembly plusthe contained casting is removed from the machine and the compacted moldmass removed, in any suitable manner, as by breaking with chisels,hammering, or in any other way. The casting will be found to beperfectly sound and to have a smooth surface finish, which is free fromvoids, and which, as indicated above, will require, at the most, but alap finish or grinding to perfect it for use.

While mm has been mentioned as a preferred refractory material, suitablefor use as a mold mass, the invention comprehends the use of otherrefractory mold materials, including magnesia, alumina, tungstendioxide, bauxite, zirconia, chromite, and a wide variety of refractorymaterials. The binding agent will be chosen with a view to itspossessing the capacity of decomposing underheat, and, at the same time,of combining with the materials forming the mass of the mold. The moldsheaths are preferably made of seamless tubing of suitable shapes andsizes, and are so conformed as to be capable of being inserted in eachother to provide any desired length of finished mold; the excess lengthsbeing removed after the mold material has been compressed into place inand about the fusible metal pattern.

The patterns may, as indicated above. be made in any desirable manner,as by machining, grinding, and the like, and, in the case of relativelysimple shapes, which are free from or characterized by very littleundercutting, as noted above, plaster of Paris molds may be used, whichcan be destroyed when removing the cast fusible metal pattern.

Referring now to the drawing, there is shown the details of an apparatussuitable for carrying out the teachings of the present invention, itbeing understood that the disclosures are presented by way of exampleonly, as it is obvious that other specific devices may be made use of inthe practice of the present invention without altering the scopethereof, and it is not intended to be limited to the structures hereshown and described, except as such limitations are clearly imposed bythe appended claims.

In the drawing, like numerals refer to similar parts throughout theseveral views, of which Fig. 1 is a vertical section of a mold assemblywith the pattern in place, and immediately prior to the compressionstep;

Fig. 2 is a view similar to Fig. 1 showing the completion of thecompression step;

Fig. 3 is an elevation of one-half of a two part mold holder; N

Fig. 4 is a top plan view of a centrifugal casting machine with moldholders disposed therei Fig. 5 is an end view of the interior of a pumpcasing showing a plurality of screw pump elements in operative position,and

Fig. 6 is an elevation of a screw threaded cast pump member.

Referring more specifically to the drawing, the invention will bedescribed with particular reference to the casting of drill tips andscrew pump elements from high melting metal compositions such as onecontaining 65% tungsten carbide and 35% cobalt, nickel or iron, or amixture thereof.

In the drawing, numeral 10 designates a fusible metal pattern of a drilltip, which is mounted on a mold base 11 having a centering pin 12. Amold casing or sheath 13 is disposed in the base 11, lugs or ridges 14serving to center the same. An extra mold member 15 is fitted onto themember 13, a slip joint 16 permitting the locking or aligning of the twomold members. Into this mold chamber, thus formed, a mass of refractorymaterial 1'1, comprising silica flour, or the like, of 200 mesh orliner, and moistened with from 2% to 5% of sodium silicate, is inserted.Sumcient amounts of the material 17 are placed into the mold so thatwhen successively compressed by the plunger of piston 18, the upperlevel of the finally compressed material will attain the level of thetop of the pattern 10. In this connection, it is to be noted that thebottom mold members 13 are preferably so formed as to approximate ,theheight of the patterns disposed therein.

Referring to Fig. 2, the same general construction is shown with thepiston being shown at the end of the compression stroke and reaching toThe castings thus formed, whether of mmthe top of the pattern-- 20,which is shown as a gear screw element of the pump shown in Fig. 5.The'compressed mold material is designated as 17a, to differentiate itfrom the uncompressed material 17 of Fig. 1, the excess of the latterbeing designated as 17b.

The pistons or plungers 18 are preferably hollow, the central cavitybeing of such a size and shape to approximately conform to the diameterof the pattern of the article to be cast. This construction permits theforcing of the excess refractory material down the sides of the patternand into intimate contact with all the undercut portions thereof,whereas a flat faced piston or plunger would cause the excess material,17b, immediately above the pattern, to be compressed on top thereof, andnot into intimate contact with the sides.

The mold assembly, comprising the sheath 13, the compressed refractorymaterial 17a, and the enclosed pattern 20, or 10, as the case may be, isthen placed in an oven or furnace, such as a core baking oven, andheated until the mold material is set. During this heating, the bindermaterial will be driven oil! and/or decomposed, and serve as a bond forthe particles of the refractory material, while, at the same time themetal of the fusible pattern member will liquefy and fiow out from themold. This will leave the mold surfaces clean and an exact counterpart,in reverse, of

the pattern. The mold sheath 13, with the contained compressedrefractory material l'la, and the pattern member 20, is inserted in atwo part holder 30.

having symmetrical tops and bottoms 31, provided with pins 32 andsockets 33 to assure proper alignment of the several parts. The holders30 are provided with cutout portions or cavities 34:, which are adaptedto receive the sheath members 13 in a snug fit when the two parts of themold holder are placed in position. The mold holders 30 with thecontained molds 13, are placed in position in the centrifuge 40, havinga rim 41, recessed, if desired, as indicated at 42 to receive theblocked off ends 35 of the mold holders. Centrally of the centrifuge,there is provided a ring 43 of any suitable refractory material, whichring is provided with a plurality of apertures 44 opening into thecasting chambers formed in the centers of the mold assemblies.

when the centrifuge is set in operation and a mass of refractory metal,such as a composition comprising substantially tungsten carbide, and 35%cobalt, which has been heated to a temperature of incipient fusion, suchas of the order of 1400 C. and above, depending on the compositionandpercentages of the constituents, is placed in the center 45 of thecentrifuge and under the conditions of operation is immediately forcedinto the mold cavities under pressures of the order of 5 to 6 tons persq. in., more or less, depending upon the distance of throw and thespeed of the machine. The material cast is preferably, as noted above,heated to an incipiently plastic condition, in which condition, it maybe removed readily from the crucible or other container, as has not beenfound to be the case where higher temperatures are used to produce asemiplastic or viscous mass which adheres to the crucible walls.

As already noted, castings so prepared are all of uniform density. and,owing to the fineness of the construction of the mold material, and themanner in which it was prepared, the surfaces would require but a lapfinish for use.

cate shape or simple shape, where made from tungsten carbide or otherhigh melting carbides, such as those of molybdenum, vanadium, chromium,tantalum and the like, admixed or alloyed with any metal or alloycompositions, will, as already stated, be found to have a smooth surfacefinish and uniform texture and finished structure,

while exhibiting structural and physical characteristics in the way oftensile strength, which are not found in so called sintered masses oftungsten carbide and/or its alloy compositions. The final pressure stepinvolved in the formation ofsuch high refractory metal or metalloidcompositions permits the securing of articles of uniform crystallinestructure characterized by sharper cleavage and breaking as opposed tothe conchoidal fractures indicative of planes of cleavage, due topreferred orientation of crystals, as found in sinteredproducts'generally.

Referring to Figs. 5 and 6, there is shown a pump casing 50 in which aredisposed at driving screw 20, having in engagement therewith a pair ofidler pump screws 21, which are formed in the same manner as the member20. Due to the formation of these members from high refractory, abrasiveand corrosion resistant materials such as the 65% tungsten carbide and35% cobalt.

'composition disclosed, or other suitable compositions, pressure pumpsmay now be made which can handle corrosive materials such as sea water,brine and a variety of chemicals as well as slur- 4 rice and fluidscontaining abrasive materials in suspension, as may be found in bilgewater of vessels. The helical impeller blades for use in this type ofpump have been extremely short lived in screw pumps, some of the hardeststeels, when formed up into screw pump elements and used in pumps forhandling biige'water, having been found to have a life of the order ofonly a few weeks in actual service.

It will now be appreciated that there has been provided an improvedprocess for readily and accurately forming intricate shapes of all kindsfrom high melting materials of the type of tungsten carbide and itsvarious alloy combinations and other like materials, which processpermits a desired smooth finish and texture to be imparted to the castarticles without requiring the use of extraneous apparatus. In addition,there has been disclosed a novel abrasion and corrosion resistant pumpand helical impelling elements therefor, which pump, due to thelongevity of the improved refractory metal parts exceeds in performanceanything hitherto available, and thus makes available for heavy dutywork, an otherwise highly efiicient pumping device.

What is claimed is:

1. The improved method of preparing smooth surfaced molds for use inpressure casting incipiently fused, high melting refractory metalliccompositions, such as carbides of the metals of the VI Periodic Groupcomprising forming a fusible metal pattern of the article to be cast,dampening a powdered refractory having a melting point of the order of1500 C. and above, compressing the so prepared refractory material aboutthe pattem and in a metallic mold casing at a pressure above thecalculated casting pressure of the refractory metallic compositions,baking the mold assembly and melting out the pattern metal.

2. In the preparation of molds for use in casting high meltingrefractory metallic compositions such as carbides of metals of the VIPeriodic Group to form intricate shapes, the steps comprising moulding apowdered refractory about a fusible pattern and under high pressureabove the calculated casting pressure of the refractory metalliccompositions, and thereafter melting out the metal of the pattern whilebaking the mold.

3. An improved process for pressure castin intricate shapes from metalsand alloy compositions melting at temperatures of 1500' C. and above,comprising forming a fusible metal pattern of the article to be cast,ramming up a powdexed refractory mold material about the pattern in acontinuous metal sheath and under pressures of the order of 50 to 100tons per square inch and above, baking the mold and contained pattern attemperatures sufilcient to fuse the metal of the pattern, and compresingthe high melting metal composition into the finished mold and atpressures of at least one or more tons per square inch.

4. An improved process for pressure casting intricate shapes from metalsand alloy compositions melting at temperatures of 1500" C. and above,comprising forming a fusible metal pattern of the article to be cast,ramming up a powdered refractory mold material about the pattern in acontinuous metal sheath and under pressures of the order of 50 to 100tons per square inch and above, baking the mold and contained pattern attemperatures sufllcient to fuse the metal of the pattern, heating a massof a high melting metallic composition to about the temperature ofincipient fusion of the mass, placing the so heated mass in the moldaperture, and compressing the high melting metal composition into thefinished mold and at pressures of at least one or more tons per squareinch.

5. An improved method for making molds for casting high meltingrefractory metal compositions such as carbides of metals of the VIPeriodic Group, comprising forming a fusible metal pattern of thearticle to be cast, setting up the pattern in a mold casing and spacedtherefrom, compacting a pulverized refractory having a decomposablebinder in a mold and about the said pattern at pressures above thecalculated casting pressures of the refractory metallic compositions,said refractory being introduced into said mold and compacted inbatches, and thereafter heating the mold and contained refractory andpattern at temperatures sufilcient to bake the mold material and to meltthe pattern.

thereafter heating the mold and contained re-- fractory and pattern attemperatures sufficient to bake the mold material and to melt thepattern, inserting said baked mold member in a centrifugal machine andcasting a refractory metal composition in said mold and at pressures ofthe order of from 1 to 10 tons per square inch.

7. In the preparation of molds for use in casting high-meltingrefractory metal compositions such as carbides of metals of the VIPeriodic Group, to form intricate shapes, the steps comprising moldingpowdered magnesia dampened with a decomposable binder such aswater-glass about a fusible pattern and under high pressures above thecalculated casting pressure of the refractory metallic composition, andthereafter melting out the metal of the pattern while baking the mold.

8. An improved method of casting refractory metal compositions, such ascarbides of metals of the VI Periodic Group, comprising forming afusible metal pattern of the article to be cast,

setting up the pattern in a mold casing and spaced therefrom, contactingpulverized magnesia dampened with water-glass in the mold and about thesaid pattern and at pressures above the calculated casting pressures ofthe refractory metallic compositions, said magnesia and water-glassbeing introduced into said mold and compacted in batches, thereafterheating the mold and contained pattern at temperatures sumcient to bakethe mold material and decompose the water-glass and to melt out thepattern, inserting said baked mold member in a centrifugal machine andcasting a refractory metal composition in said mold and at pressures ofthe order of from 1 to 10 tons per square inch and above.

ETIENNE A. DE BATS.

